The present invention relates to a compounding method for reducing speckle noise, and more particularly to a compounding method for reducing speckle noise applied in an ultrasound imaging apparatus.
The inherent target-detection capability of coherent imaging system is severely degraded by the presence of speckle. Speckle is the result of constructive and destructive interference and appears as a random mottle superimposed on an image. Thus, it will obscure the detail of image. Hence, this degradation is especially objectionable in diffraction limited ultrasonic imaging system.
Speckle in coherent optical or acoustical images can be reduced by a number of methods including spatial compounding and frequency compounding methods. Furthermore, both spatial and frequency compounding methods are tried to achieve the speckle noise reduction by increasing the decorrelation between speckle patterns of the same object. For the spatial compounding method, the speckle decorrelation is achieved by imaging the same target object from different angles. That is, when the relative distance between the target object and the transducer of imaging apparatus is changed, the speckle decorrelation can be increased. On the other hand, for the frequency compounding method, the speckle decorrelation is achieved by imaging the same target object within different frequency ranges.
Those compounding methods according to the prior arts can increase the decorrelation to reduce the speckle noise in the image, however, the prior arts reduce the speckle noise at the price of significant degradation in spatial resolution. For the spatial compounding method, the spatial resolution will degrade because the beam size is increased in order to measure the target object from different angles. Similarly, the spatial resolution will degrade in the frequency compounding method, because the bandwidth is reduced to result in that the pulse becomes longer.
Therefore, the purpose of the present invention is to develop a compounding method to deal with the above situations encountered in the prior art.
It is therefore an object of the present invention to provide a compounding method for reducing speckle brightness variations of the image with less spatial resolution degradation.
It is another object of the present invention to provide a compounding method for reducing speckle noise by the decorrelation between signals under different strain states.
According to an aspect of the present invention, there is provided a compounding method for reducing speckle noise applied in an ultrasound imaging apparatus. The compounding method includes the steps of providing an object, measuring the object for obtaining a reference image by the ultrasound imaging apparatus, applying an external force to the object to deform the object, measuring the deformed object for obtaining a deformed object image at the same position, estimating an in-plane displacement field of the deformed object image for correcting an in-plane motion of the object to obtain a corrected image, and compounding the reference image with the corrected image to obtain a compounded image of the object for achieving the speckle noise reduction.
For example, the ultrasound imaging apparatus is a medical diagnostic ultrasound apparatus.
Preferably, the object is a tissue, an organ or an embryo.
Preferably, the reference image, the deformed object image, the corrected image and the compounded image are composed of a plurality of pixels, respectively. Each plural pixels of the compounded image is preferably an average of each relative plural pixels of the reference image and each relative plural pixels of the corrected image, respectively.
According to another aspect of the present invention, there is provided a compounding method for reducing speckle noise applied in an ultrasound imaging apparatus. The compounding method includes the steps of providing an object which spontaneously produces deformation, measuring the object for obtaining a first image at a first time, measuring the object for obtaining a second image at a second time at same position, wherein the second image is an image of the deformed object, estimating an in-plane displacement field of the second image for correcting an in-plane motion of the object to obtain a corrected image, and compounding the first image with the corrected image to obtain a compounded image of the object for achieving the speckle noise reduction.
For example, the ultrasound imaging apparatus is a medical diagnostic ultrasound apparatus.
Preferably, the object is a tissue, an organ or an embryo.
Preferably, the first image, the second image, the corrected image and the compounded image are composed of a plurality of pixels, respectively. Each plural pixels of the compounded image is preferably an average of each relative plural pixels of the first image and each relative plural pixels of the corrected image, respectively.
According to an additional aspect of the present invention, there is provided an ultrasound imaging apparatus. The apparatus includes a detector for measuring an object to obtain a reference image at a position and measuring the object having a deformation to obtain an deformed object image at the position, and a processor for estimating an in-plane displacement field of the deformed object image for correcting an in-plane motion of the object to obtain a corrected image, compounding the reference image with the corrected image to obtain a compounded image of the object for achieving speckle noise reduction, and outputting a signal of the compounded image.
For example, the ultrasound imaging apparatus is a medical diagnostic ultrasound apparatus.
Preferably, the object is a tissue, an organ or an embryo.
Preferably, the deformation of object is results from applying an external force or spontaneously producing.
Preferably, the reference image, the deformed object image, the corrected image and the compounded image are composed of a plurality of pixels, respectively. Each plural pixels of the compounded image is preferably an average of each relative plural pixels of the reference image and each relative plural pixels of the corrected image, respectively.
Preferably, the ultrasound imaging apparatus further includes a device for receiving the signal of compounded image, wherein the device is a display or a printer.